Distribution of electric current in an electrolytic cell anode

ABSTRACT

IN THIN FLAT METAL ANODES A MORE UNIFORM CURRENT DISTRIBUTION IS OBTAINED BY CUTTING VERTICAL SLOTS IN THE ANODE EITHER FROM THE FOOT OR THROUGH THE FOOT OF THE ANODE AND CONTINUING UPWARD FOR ABOUT 75 PERCENT OR MORE OF THE HEIGHT OF THE ANODE BLADE, EACH SEGMENT THUS PREPARED BEING SUPPLIED WITH BUS BAR CONNECTING MEANS. THE VERTICAL SLOTS IN THE THIN ANODE SUPPRESS HORIZONTAL CURRENT FLOW. ADDITIONALLY, IN THE CASE WHEREIN THE THIN FLAT ANODE IS WELDED TO FOOT, THE POST WELD DISTORTION IS RELIEVED.

July 24, 19 73 $cHM|DT E'TAL 3,748,250

DISTRIBUTION OF ELECTRIC CURRENT IN AN ELECTROLYTIC CELL ANODE Filed Dec. 23,41971 United States Patent M 3,748,250 DISTRIBUTION OF ELECTRIC CURRENT IN AN ELECTROLYTIC CELL AN ODE John E. Schmidt, Southgate, and Robert P. Metcalfe,

Grosse Ile, Mich., assignors to BASF Wyandotte Corporation, Wyandotte, Mich.

Filed Dec. 23, 1971, Ser. No. 211,614 Int. Cl. B01k 3/10 US. Cl. 204-266 4 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND (1) Field of the invention This invention relates to electrolytic cells, more particularly to electrolytic cells adapted for the protection of chlorine and casutic, the cells being commonly known in the art as diaphragm-type cell. An anode with integral support member having an improved current distribution and minimized post weld distortion is provided.

(2) Description of the prior art For many years the typical electrolytic cell of commerce used a graphite anode. More recently as the result of considerable experimental work dimensionally stable metal anodes have come into being for use with these electrolytic cells. Typically these metal anodes are a thin fiat sheet of metal or a sheet of expanded mesh pro 'vided with some means of attachment at the bottom of the anode for attaching and connecting the anode to the bus bar means. In some of these congurations the sheet is welded to some sort of a foot which has the connection with bus bar means. However as is well known in other arts, welding introduces distortions into the anode configuration.

An additional problem which can be encountered with these metal anodes is a tendency of the electric current to flow horizontally across an anode (and develop high local current densities) in places where natural irregularities of assembly or fabrication tend to induce higher current flows. For example, due to cathode irregularities, a bump on the cathode may protrude towards the anode and provide an easier flow path for current due to the reduced electrolyte gap at that point.

Also, random irregularities in anode metal thickness, coating thickness on dimensionally stable anodes can promote local regions of higher or lower current flow. These in turn can cause locally higher coating wear rates, heat effects, more power consumption and other undesirable efiects.

It is readily recognizable that correction of these problems would allow more eflicient and effective use of metal anodes.

SUMMARY OF THE INVENTION -In accordance with this invention there is provided in a diaphragm-type electrolytic cell for the production of chlorine and caustic alkali from alkali metal chloride 3,748,250 Patented July 24, 1973 solutions and having a dimensionally stable metal anode, the lower portion thereof having a flange extending substantially perpendicular to face of said anode, said flange having means for attaching to the bus bar means in a mechanical and electrical conductive relationship therewith, the improvement comprising: segmenting said anode into equal portions such that the upper portion of the anode is left intact and said segmentation is along vertical lines (with respect to the height of said anode) which commences at said flange whereby electrical current distribution is caused to flow vertically up said anode rather than across said anode.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a side view of a flat metal anode which has been slotted in accordance with this invention. FIG. 2 is a cross-sectional end view of FIG. 1 taken along lines 2-2 showing the installation detail of the metal anode.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the invention as shown in FIG. 1 there is provided an anode having an anode blade portion 10 and flange portion 12 and which is attached to the electrolytic cell by means of stud bolts 14. It is to be noted that anode blade 10 has been cut or slit for approximately threefourths of the distance from the flange upward to the top of the anode blade 10. It is to be recognized, of course, that there are conditions under which the slit can be more than the foregoing approximation of Depending on the materials of construction of the anode the slit can be even closer to the tip provided the tip of the anode blade retains its strength, alignment and cohesiveness. -It should be further noticed that each of the cuts (or slots) is equally spaced between the stud bolts 14.

To aid one in the use of the anode of this invention FIG. 2 illustrates the typical installation of the anode. Cell bottom 18 which is made of any suitable strength carrying metal is covered with a non-conductive layer 16, both cell bottom 18 and non-conductive layer 16 having holes in axial alignment for insertion of stud bolt 14 which holds anode flange 12 firmly against nonconductive layer 16. The threaded end of stud bolt 14 extends through the cell bottom 18 into and through bus bar means 20. The stud bolt 14 is held in mechanical and electrical connection by the use of flat washer 22 and stud nut 24. It is well within the skill of the art to use a beveled washer with a corresponding chamfer in bus bar means 20 or to omit the use of washer 22 and use only stud nut 24 which may be either flat or beveled as desired.

In FIG. 1 the invention has been illustrated wherein flange 12 is continuous, however, flange 12 can also be segmented or slotted by extending the slot of anode blade 10 to and through flange 12. Extending the slot through flange 12 is particularly advantageous when anode blade 10 and flange 12 are not formed from the same sheet of metal but instead blade 10 is welded to flange 12. When flange 12 is a separate piece of metal it may be desirable that the original flange 12 be made of angle metal having a right angle. Extending the slot through flange 12 as indicated by the dotted lines 32 in FIG. 1 will relieve the post weld distortion which can be introduced into the anode. Additionally it should be recognized that while a solid metal blade 10 has been shown in FIGS. 1 and 2 that it is within the scope of this invention to use an expanded mesh sheet or other configurations in place of the solid metal sheet shown.

The non-conductive layer 16 can be any of the well known lining materials of the prior art including but not limited to, as applicable using ordinary engineering skills, asphaltic mastics, rubber, chlorinated plastics and polymers and copolymers of trifluorochloroethylene, tetrachloroethylene and tetrafluoroethylene sold under trade names such as Teflon and Kel-F.

The blade portion of anode is typically fabricated from a corrosion resistant metal such as titanium and then coated with a very thin coating of a material or alloy of materials which will enhance its electrical conductivity and release of chlorine. The flange of anode 12 on the other hand, need not contain the coating. The flange 12 after being so shaped contains not more than 10 percent of the surface of one side of the anode. While a solid anode blade 10 has been illustrated, it is within the scope of this invention to also have the blade of expandable mesh material so as to facilitate the formation of gas bubbles. With respect to the present invention whether the anode blade 10 is a solid sheet or expanded metal is immaterial. Typically the thickness of sheet being utilized is from about 0.040 to about 0.141 inch.

Two or more holes are drilled in the flange and studs are welded thereto in such a manner that a good electrical connection is obtained. The exact number of studs or bolts is a matter of choice depending upon the length of the anode and the size of the bolts employed with respect to their electrical current carrying capacity.

The anode of this invention has been described in terms of fabrication from titanium metal since in terms of availability and cost it is the metal of choice. But this is not to imply or mean that the anode can only be made out of titanium, rather than other valve metals and/or alloys thereof can be used. A specially suitable restrictive group of valve metals is titanium, tantulum and niobium. Preferably titanium is employed and it is normally a commercially pure grade. Alloys of titanium may be employed as long as the alloy meets the criterion of passivity, that is metal alloys which become passivated when polarized anodically and remain passive well beyond the anodic potential needed to convert the chloride ion to chlorine. The phenomenon of passivity in this connection is discussed in an article by Greene, appearing in the April 1962 issue of Corrosion, pp. 136-t to l42-t wherein reference may be made to FIG. 1 of the article which describes typical active-passive transition of the metal towards a corrosive medium. Titanium alloys of aluminum, vanadium, palladium, chromium or tin can be employed in which the latter metals are present as less than 10 percent of the alloy.

While it is beyond the scope of the present invention, it is known in the art to coat metal anodes with an oxide coating so as to improve the performance of the anode. Typically these coatings are based on oxides of metals from the platinum group, or gold or silver or similar materials either alone, in combination with two or more or in combination with a valve metal. Elucidation of these techniques may be had by reference to patents such as British Pat. 1,195,871 or British Pat. 1,235,570.

To those skilled in the art many other modifications and ramifications will naturally suggest themselves based on this disclosure. These ramifications and modifications are intended to be comprehended as within the scope of this invention.

Having thus described the invention, what it is desired to claim and secure by Letters Patent is:

1. In a diaphragm-type electrolytic cell for the production of chlorine and caustic alkali from alkali metal chloride solutions and having a dimensionally stable metal anode, the lower portion thereof having a flange extending substantially perpendicular to the face of said anode, said flange having means for attaching to the bus bar means in a mechanical and electrical conductive relationship therewith, the improvement comprising:

segmenting said anode into a plurality of equal vertical portions in such a manner that the free unattached end of the anode is left intact and connects each portion into a unitary anode blade tip, said segmentation is along vertical lines (with respect to the height of the anode) said segmentation commencing at said anode flange (or attached end), whereby electrical current distribution is caused to flow vertically up said anode rather than across said anode.

2. The anode of claim 1 wherein the slit extends upward for about percent of the height of the anode.

3. The anode of claim 1 wherein the anode is attached to the bus bar means by studs attached to the flange and there is one segmentation equally spaced between each consecutive pair of studs.

4. The anode of claim 3 wherein the segmentation extends across the flange.

References Cited UNITED STATES PATENTS 3,591,483 7/1971 Loftfield et a1 204266 1,798,575 3/1931 Allen et a1. 204-266 961,549 6/ 1910 Sperry 204-284 3,085,969 4/ 1963 Motock 204-283 FOREIGN PATENTS 1,125,493 8/1968 Great Britain 204-266 JOHN H. MACK, Primary Examiner W. I. SOLOMON, Assistant Examiner US. Cl. X.R. 204-252, 284 

